1. Field of the Invention
This invention relates to a method which employs an improved mask for forming micro-multi-layer metallization films of high intimacy and dimensional precision through ion plating or sputtering.
2. Description of the Prior Art
When circuits and circuit elements are formed by means of thin film integrated circuit fabrication techniques, it is a general practice, to form electrically conductive members and insulator films by vacuum deposition, sputtering, ion plating or like methods. Although films formed by vacuum deposition have greatly inferior intimacy with the substrate compared to those formed by sputtering or ion plating, vacuum deposition is widely used because of its ease of forming film with extremely precise patterns by the aid of masks. On the other hand, films formed by sputtering or ion plating have superior intimacy with the substrate and excellent characteristics required for stacking up on step covering portions inherent in multilayer metallization. With a deposition mask commonly used for vacuum deposition, however, sputtering or ion plating cannot be used to form a fine pattern with desired dimensional precision. In vacuum deposition in which evaporated particles more freely in an evacuated atmosphere having a pressure on the order of 10.sup.-.sup.4 Torr or less, the particles will have so long a mean free path as to be free from scattering, and will reach the surface to be deposited after passing through a masked pattern in a substantially straight path from the particle source. Consequently, the masked pattern is accurately transferred to the surface to be deposited. On the other hand, in sputtering or ion plating in which the multi-layer stacking of films is performed under a pressure of 10.sup.-.sup.2 to 10.sup.-.sup.3 Torr, atoms will have so short a mean free path as to tend to scatter, thereby depositing particles which scatter into the slight gap between the surface to be deposited and the mask. Therefore, no industrial processes for masked deposition by means of sputtering or ion plating have yet been established. In order that a precise deposited pattern be formed by sputtering or ion plating, a lift-off process may be employed in which sputter deposition is effected onto a surface to be coated that has a mask pattern previously formed by vacuum deposition and the mask pattern is subsequently removed by etching; alternatively, a mask pattern of photo-resist is formed on surface which has been subjected to deposition by sputtering or ion plating and the desired pattern is formed by etching. These measures involve chemical etching processes so that chemical etching solvents and etching mask materials inevitably contributes to contamination and deterioration of the stacking material.